The present invention relates to a chip carrier device, and more particularly, to a semiconductor device including a semiconductor chip positioned within a cavity of a leadless ceramic base, and a cap for sealing the chip within the cavity.
Devices for housing semiconductor chips have been developed wherein an integrated circuit chip, for example, is placed on a leaded frame or in a cavity with a leaded or leadless base and sealed with a cap. These caps have generally been made of metal for reasons of workability, solderability, cost, etc. U.S. Pat. No. 4,445,274 discloses a mount for electronic components wherein the cap is either ceramic or metal, and is sealed with glass having a low-melting point.
In a chip carrier device incorporating base, leads, and a ceramic cap, the cap may be bonded to the base by metallizing the two in the regions of contact and soldering them in the metallized regions. Soldering is carried out by inserting a thin preformed solder ring between the ceramic base and cap, melting the solder while simultaneously pressing the cap against the base, and then cooling to solidify the solder. The pressing of the cap is required to prevent formation of voids in the soldering portion between the base and the cap since a ceramic cap is often somewhat warped.
One problem associated with soldered caps is that excess solder flows from the heated seal into the cavity of the base and outside the cap, resulting in possible short-circuits or solder particles inside with the semiconductor device. The presence of solder flux within the sealed cavity can result in corrosion of the cavity contents.
The U.S. Pat. No. 4,626,960 discloses a semiconductor device comprised of a ceramic body with a semiconductor chip mounted thereon and a ceramic cap sealed to the ceramic body with solder. This device incorporated a soldered ceramic cap wherein excess solder is retained by a metallized side wall of the ceramic cap.
The insulating base and the insulating cap of this device have patterns of metallization in areas of contact between these components. The pattern of metallization of the insulating cap extends from the area of contact with the base to the side surfaces of the insulating cap. The insulating base and insulating cap are soldered to each other in the areas of the patterns of metallization. However, this device utilizes leads which increases the cost and complexity of the device. The base has a layered structure to provide for the connection of the leads to the chip within the base. For semiconductor devices in which leads are provided on one side of the base, provision for a heat sink at the rear of the base is often not possible. Another problem is that devices are often mounted close to the board making it difficult to remove excess solder and flux around the leads.